if strcmp(signal, 'off') 
I = std_IQ*randn(M, N) ; 
Q = std_IQ*randn(M, N) ; 
X2 = I.^2 + Q.^2; 
X2max(j) = max(max(X2));
elseif strcmp(signal, 'on') 
dtau = tau(j) - tau_tilda_m; 
domega = omega(j) - omega_tilda_m; 
I = A*L/2 * ro(dtau) .* sinc(domega*T/2 /pi) .*cos(domega*T/2 ...
+ dphi(j)) + std_IQ*randn(M, N) ; 
Q =- A*L/2 * ro(dtau) .* sinc(domega*T/2 /pi) .* sin(domega*T/2 ...
+ dphi(j)) + std_IQ*randn(M, N) ; 
X2 = I.^2 + Q.^2; 
X2max(j) = max(max(X2)); 
end